Replicator-type bubble domain generators have been improved in the art and now use combinations of magnetic elements and/or current carrying conductors to assist the replicate function. For example, current-controlled disk replicators are described in U.S. Pat. Nos. 3,611,311 and 3,735,370. The principle of operation of this type of replicator is the same as the basic disk replicator described in U.S. Pat. No. 3,555,527. However, the magnetic field produced by current in an associated conductor is used to enhance the splitting of the seed domain.
In the fabrication of current controlled replicators, designs have been provided using a magnetically soft material, such as permalloy, for both the magnetic propagation elements and for the current carrying conductor. Such a design is shown in U.S. Pat. No. 3,810,133, where a fine grained permalloy pattern is used to move bubble domains and an intersecting permalloy conductor is used to carry electrical current. Another patent showing the passage of electrical current through conductor lines and then through permalloy in U.S. Pat. No. 3,781,833. An all-permalloy current assisted disk generator is shown in P. K. George, IEEE Trans. on Magnetics, MAG-10, p. 1136, December, 1974.
In the design of complete magnetic bubble domain chips, it is often necessary to provide current carrying conductors in different portions of the magnetic chip. For example, such current carrying conductors are often used to assist the transfer of bubble domains from one shift register to another. In such transfer switches the non-magnetic conductor, typically gold, is located in a layer beneath the magnetic layer which provides the propagation elements which move the bubbles domains in response to the reorientation of a magnetic field in the plane of the magnetic layer. Copending application Ser. No. 863,829, filed Dec. 23, 1977, describes a process and structure in which a conductive layer is located beneath a magnetic layer and in which portions of the conductive layer are replaced by an electrically insulating material. In particular, this is done in the regions of the bubble detectors and generators.
In a bubble storage chip using a single high resolution masking level to define the magnetic layer and the non-magnetic current carrying conductors, the space between the bubble domain material and the magnetic drive layer is usually occupied by a non-magnetic conductor through which electrical current is passed for control of bubble transfer, generation, and replication. As bubble domain devices are scaled down so that higher densities can be obtained, it is necessary to reduce the distance between the bubble material and the magnetic drive layer, while maintaining the magnetic drive layer thickness approximately constant. An analysis of this is provided by G. S. Almasi et al in IEEE Transactions on Magnetics, MAG-12, p. 160 (1976). As a result of this, very high density bubble devices have spaces for conductor metallurgy between the bubble material and the magnetic drive layer which are thinner than the magnetic drive layer itself. Due to electromigration in current carrying materials, at some bit density it becomes possible to pass more current through the magnetic drive layer than through the conductor layer. Nevertheless, a conductor layer is generally desirable since it lowers the resistance of current carrying lines, thus reducing the power dissipation in the device. As an example, the resistivity of permalloy (NiFe) is approximately ten times that of gold.
As mentioned previously, the design of a complete magnetic bubble chip may require current carrying conductors under magnetic drive layers in certain regions of the chip. Heretofore, a good disk replicator has not been provided for use in such a magnetic chip. Accordingly, it is a primary object of the present invention to provide an improved replicate-type bubble generator having good margins, which can be manufactured by single masking level techniques, and which can be used in a magnetic chip having a non-magnetic conductor layer and a magnetic layer thereon.
It is another object of this invention to provide an improved current-controlled disk replicator which can be fabricated using single masking level processes and which exhibits good bias field and drive field margins, when used in a magnetic chip having two levels of metallurgy as described previously.
It is yet another object of the present invention to produce a magnetic storage chip characterized by a current carrying conductor layer located between a bubble domain material and a magnetic drive layer, where the magnetic chip includes a disk replicator which can be fabricated by a single level masking process.
It is a further object of the present invention to provide a single masking level disk replicator using an electrical current to assist splitting of a seed domain, which is particularly suited for the generation of bubble domains having diameters 2 microns and less.
It is a further object of the present invention to provide an improved disk replicator suitable for use in magnetic bubble chips having high density devices thereon, where operation of the disk replicator is not adversely affected by electromigration.